The invention relates to a self-pumping spring and damper unit with automatic ride level control for chassis of vehicles, in particular for motor vehicles or motorcycles, which is articulated at one articulation point on the body and at the other articulation point on the chassis and the damping unit of which has at least two working spaces which are connectable by means of a throughflow throttle valve and which contain a damping and/or springing medium which, during the jounce and rebound of the vehicle, is exchanged, damped by the throttle valves, between the working spaces, the spring and damper unit having at least one pump which is driven by means of the distance between the articulation points which varies as a result of the jounce and rebound of the vehicle, said pump generating a pressure rise in the damping and/or springing medium, with the result that the spring and damper unit maintains a fixed level in the event of a variable load on the vehicle, the pump consisting essentially of two pump parts which are movable in relation to one another and reduce a compression space and of which one pump part is connected to one articulation point and the other pump part to the other articulation point such that the distance between the articulation points which varies during the jounce and rebound of the vehicle is transferred as a compression stroke to the distance of the pump parts from one another.
Such self-pumping ride level control systems are known in connection with hydraulic dampers, in particular also in pneumatic suspensions with hydraulic dampers.
DE AS 1 209 891 discloses, in this respect, a hydropneumatic spring suspension for vehicles which connects a ride level control system for a pneumatic spring to a hydraulic shock absorber device. In this case, the hydraulic fluid serves for transmitting the forces to be absorbed to the gas cushion. The hydraulic fluid can be pumped to and fro between a reservoir and the fluid space of the springing part with the aid of a piston/cylinder arrangement, the pumping movement being generated as a result of the jounce, that is to say the springing movements, of the vehicle. The pump chamber provided in this case is an annular space between a cylinder inner wall and a piston rod, which space is connected to a reservoir and to the fluid space via inlet and outlet valves.
DE 195 47 536 A1 discloses a self-pumping hydropneumatic spring strut with internal ride level control, in which, as a result of the springing movement of the vehicle, damping medium is conveyed from a low-pressure chamber into a high-pressure chamber separated from the latter by a piston, and the two chambers are provided with pressure-accumulating gas cushions. Here, too, the pumping movement is generated by a pumping rod which penetrates into a cavity of the piston rod and which, by being tied up to the remaining damper components, transmits the springing movement of the vehicle. Here, too, oil is pumped in order to displace the ride level position. The enclosed gas volume is not changed—it has merely been compressed beforehand as a result of the increase in load.
These hydraulic dampers, in the past used almost exclusively for passenger cars with pneumatic spring systems/hydropneumatic spring systems, have recently been replaced increasingly by pneumatic spring and damper units, in which both springing and damping take place by means of a gaseous medium. Such pneumatic spring and damper units serve as particularly convenient spring suspension elements in vehicles and give a pleasant ride sensation in a spring suspension which can be adapted between a “soft” and “hard” suspension behavior, depending on road conditions.
However, whereas the previous solutions with hydraulic dampers could also be designed as simple self-pumping hydropneumatic spring struts with internal ride level control, as shown in the prior art, this was not previously the case with regard to straightforward pneumatic spring and damper devices. In the latter, as a rule, ride level control is carried out by means of a separate ride level control system which, in addition to the actual pneumatic spring and damper devices, that is to say the spring elements on the vehicle wheels, has a multiplicity of sometimes electrically operated accessories, such as pumps, accumulators, valves, etc., which all have to be accommodated in the vehicle. Furthermore, the previous simple solutions of self-pumping hydropneumatic spring struts with hydraulic dampers cannot be used for pneumatic dampers because of the compressibility of the gas.
The object of the invention, therefore, was to provide a simple self-pumping spring and/or damper unit with automatic ride level control, which can be used both as a ride level-controlled pneumatic spring for hydropneumatic spring struts and for pneumatic spring and damper devices, hence in which both the spring devices and damper devices operate with a compressible medium, said spring and/or damper unit having a compact type of construction which operates essentially without the additional assemblies of a ride level control system and which can therefore also be used easily for smaller vehicles and two wheelers.